As an alternative or in addition to the treatment of the cardiac rhythm disorders, a biventricular pacing has been proposed for some myocardium contraction disorders observed in patients suffering from heart failure, which disorders are spontaneous or induced by a traditional pacing technique. One can refer, for example, to a study from J. C. Daubert et coll., Stimucoeur, 25, #3, pp. 170-176 which gives a global overview of the topic. This therapy often induced spectacular results for patients suffering from class III heart failure and not improved by traditional treatments.
A CRT pacemaker is, for example, disclosed in the EP 1 108 446 A1 (and its counterpart U.S. Pat. No. 6,556,866 B2) (ELA Medical), which describes a device able to establish a variable interventricular delay between the two ventricles, tuned so as to resynchronize the ventricle contractions with fine optimization of the patient Haemodynamic.
Many currently used CRT devices are “multi-site” prostheses in which coils are implanted in a plurality of distinct sites, including at least one atrial site in addition to the right and left ventricle sites, as in the so-called “triple chamber” (dual ventricular pacing and sensing/pacing of the right atrium) or “quadruple chamber” (dual ventricular pacing and dual sensing/pacing of the atriums) devices. There are also multi-site devices where one of the ventricle leads is implanted in the right ventricular apex and the other in a position chosen to optimize the ventricular resynchronization.
One can define “pacing sites” as the physical location where the intra-cardiac electrodes are in the myocardium. Those sites can be chosen during the implant procedure by an appropriate positioning of the electrodes. When the device comprises several electrodes in a same cardiac cavity, a modification of the pacing site is then possible by an internal switching inside the device.
The notion of “pacing sequence” is related, on one hand, to the order in which the pacing pulses are delivered to the heart (for example: atrium first, then left ventricle, then right ventricle) and, on the other hand, to the timings between the application of these various successive pulses. The pacing sequence is defined at implant and can be, if necessary, subsequently changed by appropriate internal switches of the device and by adjustments of the pacing sequence parameters.
One can define the “pacing configuration” as the combination of the characteristics related to the “pacing sites” and of those related to the “pacing sequence”.
It is necessary to evaluate the relevancy of the selected pacing configuration, for this impacts the efficiency of the bi-ventricular pacing therapy. Furthermore, the positive effects procured by this therapy can lead, in the long term, to re-evaluate the initial configuration to eventually change the sites and/or the pacing sequence parameters.
The ultrasound-based evaluation techniques that shall be implemented in the hospital environment by a qualified personnel are expensive and can not be used as often as necessary without interfering with the daily life of the patient.
A solution described in the aforementioned patent EP 1 108 446 A1 concerns in evaluating the degree of synchronization of the right and left ventricle contractions by an intra-cardiac bio-impedance measurement. This data are indeed representative of the cardiac flow and, therefore, of the ejection fraction, considered as being the reference Haemodynamic parameter.
The present invention is based on another approach of the optimization of the bi-ventricular pacing, implementing an analysis of the endocardiac acceleration, and more precisely an analysis of the endocardiac acceleration peaks.
Indeed, clinical studies have indicated that the endocardiac acceleration is a parameter that provides very comprehensive information of the myocardium functional state, in the case of a normal functioning as well as in a deficient one: the endocardiac acceleration, which is measure by an accelerometer directly in contact with the cardiac muscle (generally, but not exclusively, at the right ventricle apex, sometimes in the right atrium) very precisely reflects, in real time, the converging phenomenon of the mechanical functioning of the heart.
More precisely, the EP 0 515 319 A1 (and its counterpart U.S. Pat. No. 5,304,208) (Sorin Biomedica Cardio SpA) teaches a useful manner to collect the endocardiac acceleration signal by means of an endocardiac lead equipped with a distal pacing electrode implanted in the ventricle and integrating a micro-accelerometer allowing to measure the endocardiac acceleration. The endocardiac acceleration signal collected during a cardiac cycle presents two peaks, corresponding to the two major sounds that it is possible to identify in each cycle of a healthy heart:                the first endocardiac acceleration peak (“PEA1”) corresponds to the closing of the mitral and tricuspid valves, at the beginning of the iso-volumetric ventricular contraction (systole). The variations of this first peak are narrowly linked to the pressure variations in the ventricule (the amplitude of the PEA1 peak being, more precisely, correlated to the positive maximum value of the pressure variation dP/dt in the left ventricle) and can therefore constitute a representative parameter of the myocardium contractility, which is linked to the activity level of the sympathetic system;        the second endocardiac acceleration peak (“PEA2”) corresponds to the closing of the aortic and pulmonary valves, at the moment when the iso-volumetric ventricular relaxation occurs. This second peak, induced by the rapid deceleration of the blood mass moving in the aorta is a representative parameter of the protodiastolic blood pressure in the beginning of the diastole.        
The EP 0 655 260 A1 (and its counterparts U.S. Pat. No. 5,693,075 and U.S. Pat. No. 5,496,351) (Sorin Biomedica Cardio SpA) describes a useful manner to process the endocardiac acceleration signal delivered by the sensor located in the end of the lead to deliver two values linked to those respective endocardiac acceleration peaks. These values are notably useful for the detection of cardiac rhythm disorders and whether or not to trigger a defibrillation therapy.
The EP 1 736 203 A1 (and its counterpart FR 2 887 460 A1 and U.S. patent application Ser. No. 11/425,668 filed Jun. 21, 2006) (ELA Medical) describes an application specific to bi-ventricular implantable pacemakers, using the parameters linked to the endocardiac acceleration to determine an optimal pacing configuration for the patient, during implant or after. Various measurements are performed to characterize the PEA signal and are combined to give a composite performance indication, the final pacing configuration chosen being the one that maximizes this performance indication.